DOCSLIB.ORG

The Retinal Fate of Xenopus Cleavage Stage Progenitors Is Dependent Upon Blastomere Position and Competence: Studies of Normal and Regulated Clones

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Retinal Fate of Xenopus Cleavage Stage Progenitors Is Dependent Upon Blastomere Position and Competence: Studies of Normal and Regulated Clones The Journal of Neuroscience, August 1993, f3(8): 31933210 The Retinal Fate of Xenopus Cleavage Stage Progenitors Is Dependent upon Blastomere Position and Competence: Studies of Normal and Regulated Clones Sen Huang and Sally A. Moody DeDartment of Anatomv and Neuroscience Proaram, The George Washington University Medical Center, Washington, D.6. 20037 The clonal origin of the stage 43-44 Xenopus retina from neighbors. This result suggests that dorsal-animal blasto- cleavage stage precursors was quantitatively assessed with meres change positional values in only one direction (dorsal lineage tracing techniques. The retina descends from a spe- to vegetal) after neighbor cell deletion, and that retinal fate cific subset of those blastomeres that form forebrain. The is dictated by blastomere position. To test this hypothesis most animal dorsal midline cell (Dl .l. 1) produced about half directly, different ventral and vegetal blastomeres, which of the retina, the three other dorsal ipsilateral blastomeres normally do not produce retina, were transplanted to the each produce about an eighth of the retina, and the four position of D 1.1.1. The progeny of ventral equatorial blas- contralateral dorsal blastomeres and an ipsilateral ventral- tomeres (Vl .1.2 and V2.1.2) populated the retina in a pattern animal cell together produce the remaining eighth of the that was indistinguishable from that of normal Dl. 1 .l, show- retina. There was no significant spatial segregation of the ing that position in the cleavage stage embryo is an important clones derived from different progenitors in either the an- determinant of retinal lineage. However, progeny of trans- terior-posterior or dorsal-ventral axes of the retina and no planted ventral- or dorsal-vegetal pole blastomeres (V2.1 .l boundaries between clones were observed. Instead, the and D2.1 .l) never populated the retina, demonstrating that clones intermixed to form multiple radial subclones that were not all blastomeres are competent to form retina. equivalent to those demonstrated by marking optic vesicle [Key words: Xenopus laevis, retina, determination, fegu- progenitor cells (Holt et al., 1988; Wetts and Fraser, 1988). lation, competence, transplantation] This mosaic pattern was initiated by the beginning of gas- trulation, advanced in the neural plate, and virtually complete The mechanismsby which a multipotent embryonic cell is de- in the optic vesicle. At optic vesicle stages cell movement termined to become one particular neuronal cell type is poorly within subclones was restricted, resulting in the formation understood in vertebrates, but it is generally believed that com- of lineally related columns of cells in the mature retina. mitment to a particular CNS phenotype occurs in a complex To determine if the blastomere progenitors are determined seriesof cellular decisionsthat affect the developmental poten- to produce these retinal lineage patterns, the major retinal tial of progenitor cells and the specific phenotypes of their prog- progenitor (D1.l.l) was deleted bilaterally. About 80% of eny (reviewed by Jacobson, 199 1; McConnell, 1991). There are the tadpoles developed normal-appearing eyes; of these the several examplesindicating that the developmental potential of retinas in two-thirds were normal in size and the rest were neuronal progenitors is gradually restricted. Cell lineage in ze- smaller. The blastomeres surrounding the deleted Dl .l .l brafish becomestissue specific during gastrulation, but becomes progenitors changed their contributions to retina in different cell type specific later (Kimmel and Warga, 1986). Cortical neu- ways to effect a complete or partial restoration. Ventral blas- rons become committed to a laminar fate at the time of their tomeres, which normally contribute mainly to the tail, pro- final mitotic division, but are not committed to a particular cell duced substantial amounts of the retina while dorsal blas- type until later (McConnell, 1991). In the retina, progenitors tomeres, which normally contribute mainly to the head, may first be restricted to produce cells in certain regions (Wil- decreased their contribution to the retina. To determine liams and Goldowitz, 1992) and then, perhaps as late as the whether these changes in retinal lineage were due to changes terminal mitosis (Turner and Cepko, 1987; Holt et al., 1988) in blastomere position after the surgery, various other blas- to produce particular cell types. tomeres were deleted prior to lineage mapping. Dorsal-an- Since the retina is accessibleto lineage tracing techniques imal blastomeres took over the retinal fate of their dorsal- during development, and is composed of a variety of easily vegetal neighbors after those neighbors were deleted, but identifiable cell types that are arranged in a highly ordered spa- did not change fate after the deletion of their ventral-animal tial pattern, it has served as a model for understanding the relationship between cell lineage and cell type determination in Received Oct. 9, 1992; revised Feb. 16, 1993; accepted Mar.. 1, 1993. the nervous system. Labeling of mitotic precursor cells in the This work was supported by NIH Grants NS23 158 and EY 10096. We thank optic vesicle or perinatal retina, either by intracellular lineage Mrs. Lianhua Yang for her excellent technical assistance. dye injection (Holt et al., 1988; Wetts and Fraser, 1988; Wetts Correspondence should be addressed to Dr. Sally A. Moody, Department of et al., 1989) or by infection with a recombinant retrovirus (Price Anatomy and Neuroscience Program, The George Washington University Medical Center, 2300 I Street, N.W., Washington, D.C. 20037. et al., 1987; Turner and Cepko, 1987; Turner et al., 1990), Copyright 0 1993 Society for Neuroscience 0270-6474/93/133193-18$05.00/O elegantly demonstratesthat most of the clones derived from a 3194 Huang and Moody - Lineage Regulation in Frog Retina single neuroepithelial cell contain more than one retinal cell To test experimentally whether these progenitors are deter- type; mitotic retinal cells rarely produce a clone consisting of a mined regarding these retinal lineage patterns, we bilaterally single phenotype. Although this fact has often been cited as deleted the major progenitor of the retina and quantified the demonstrating that cell lineage plays no role in vertebrate CNS retinal contribution of the remaining blastomeres. To test whether phenotype determination, this observation addresses only one blastomeres that normally do not produce retina are competent way that lineage may be important, that is, to produce a clone to do so if placed in the appropriate position, single labeled cells of cells having the same phenotype. There are several examples were either deleted from or transplanted into the site of the that show that cell lineage directs phenotype choices in other major retinal progenitor. The results from both approaches sup- ways (reviewed in Kenyon, 1985; Stent, 1985; Davidson, 1990). port the hypothesis that the position of a blastomere prior to Lineage patterns may direct different progenitors to produce gastrulation determines whether it will be a progenitor of the prescribed subsets of cell types, as has been shown for nematode retina, in most cases regardless of the blastomere’s original lin- motoneurons (White et al., 1982). Lineage genes may direct eage. However, some vegetal blastomeres are not competent to progenitors to divide a prescribed number of times and thus make retina even when located in the most “retinogenic” po- control the number of cells in a population (Chalfie et al., 198 1; sition. Williams and Herrup; 1985). Finally, lineage patterns may place the descendants of a particular progenitor in prescribed domains Materials and Methods of a tissue, such that their phenotypes are determined by region- Embryo collection. Fertilized Xenopus laevis eggs were obtained by go- specific cell-cell interactions. This occurs in the nematode vulva nadotropin-induced mating ofadult frogs. After the jelly coat was chem- ically removed, two- and early four-cell stage embryos with the first (Stemberg and Horvitz, 1989), and has been suggested in nu- cleavage furrow bisecting the gray crescent (Klein, 1987) were collected merous regions of the vertebrate CNS (Jacobson, 1983, 1985; for later use. At 32 cells, only those embryos with stereotypic radial Herrup, 1986; Fraser et al., 1990; Leber et al., 1990). cleavages (type X, Jacobson 198 1a; Moody, 198713) were used for lineage In order to investigate whether these other kinds of lineage dye injection, blastomere deletion, and transplantation. By selecting this patterns have a significant role in vertebrate CNS pattern for- population for study we minimized any variations in furrow pattern and thus kept blastomere position consistent among animals (Moody, mation, it is necessary to study the variation in phenotype, cell 1987a,b, 1989; Moody and Kline, 1990; Huang and Moody, 1992). In number, and spatial distribution between clones derived from other words, we were able to inject, delete, and transplant progenitors the same progenitor in many different animals. Analysis of clone that were nearly invariant among animals. variation has been a most important means for establishing the Lineage dye injection. About 1 nl of 0.5% Texas red-dextran amine (Molecular Probes) or fluorescein-dextran amine (Molecular Probes) role cell lineage plays in nematode development. In fact, the was pressure injected into identified blastomeres. Previous fate maps critical evidence
Load more

Recommended publications
  • Sperm Penetration and Early Patterning in the Mouse 5805
    Development 129, 5803-5813 5803 © 2002 The Company of Biologists Ltd doi:10.1242/dev.00170 Early patterning of the mouse embryo – contributions of sperm and egg Karolina Piotrowska* and Magdalena Zernicka-Goetz† Wellcome Trust/Cancer Research UK Institute, and Department of Genetics, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK *On leave from the Department of Experimental Embryology, Polish Academy of Sciences, Jastrzebiec, Poland †Author for correspondence (e-mail: [email protected]) Accepted 12 September 2002 SUMMARY The first cleavage of the fertilised mouse egg divides the 2-cell blastomere to divide in parthenogenetic embryo does zygote into two cells that have a tendency to follow not necessarily contribute more cells to the blastocyst. distinguishable fates. One divides first and contributes its However, even when descendants of the first dividing progeny predominantly to the embryonic part of the blastomere do predominate, they show no strong blastocyst, while the other, later dividing cell, contributes predisposition to occupy the embryonic part. Thus mainly to the abembryonic part. We have previously blastomere fate does not appear to be decided by observed that both the plane of this first cleavage and the differential cell division alone. Finally, when the cortical subsequent order of blastomere division tend to correlate cytoplasm at the site of sperm entry is removed, the first with the position of the fertilisation cone that forms after cleavage plane no longer tends to divide the embryo sperm entry. But does sperm entry contribute to assigning into embryonic and abembryonic parts. Together these the distinguishable fates to the first two blastomeres or is results indicate that in normal development fertilisation their fate an intrinsic property of the egg itself? To answer contributes to setting up embryonic patterning, alongside this question we examined the distribution of the progeny the role of the egg.
    [Show full text]
  • Human Blastocyst Morphological Quality Is Significantly Improved In
    Human blastocyst morphological quality is significantly improved in embryos classified as fast on day 3 (R10 cells), bringing into question current embryological dogma Martha Luna, M.D.,a,b Alan B. Copperman, M.D.,a,b Marlena Duke, M.Sc.,a,b Diego Ezcurra, D.V.M.,c Benjamin Sandler, M.D.,a,b and Jason Barritt, Ph.D.a,b a Mount Sinai School of Medicine, Department of Obstetrics and Gynecology, Department of Reproductive Endocrinology and Infertility, and b Reproductive Medicine Associates of New York, New York, New York; and c EMD Serono, Rockland, Massachusetts Objective: To evaluate developmental potential of fast cleaving day 3 embryos. Design: Retrospective analysis. Setting: Academic reproductive center. Patient(s): Three thousand five hundred twenty-nine embryos. Intervention(s): Day 3 embryos were classified according to cell number: slow cleaving: %6 cells, intermediate cleaving: 7–9 cells, and fast cleaving: R10 cells, and further evaluated on day 5. The preimplantation genetic diagnosis (PGD) results of 43 fast cleaving embryos were correlated to blastocyst formation. Clinical outcomes of transfers involving only fast cleaving embryos (n ¼ 4) were evaluated. Main Outcome Measure(s): Blastocyst morphology correlated to day 3 blastomere number. Relationship between euploidy and blastocyst formation of fast cleaving embryos. Implantation, pregnancy (PR), and birth rates resulting from fast embryo transfers. Result(s): Blastocyst formation rate was significantly greater in the intermediate cleaving (72.7%) and fast cleav- ing (54.2%) groups when compared to the slow cleaving group (38%). Highest quality blastocysts were formed significantly more often in the fast cleaving group. Twenty fast cleaving embryos that underwent PGD, formed blastocysts, of which 45% (9/20) were diagnosed as euploid.
    [Show full text]
  • Essential Role of Non-Canonical Wnt Signalling in Neural Crest Migration Jaime De Calisto1,2, Claudio Araya1,2, Lorena Marchant1,2, Chaudhary F
    Research article 2587 Essential role of non-canonical Wnt signalling in neural crest migration Jaime De Calisto1,2, Claudio Araya1,2, Lorena Marchant1,2, Chaudhary F. Riaz1 and Roberto Mayor1,2,3,* 1Department of Anatomy and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK 2Millennium Nucleus in Developmental Biology, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile 3Fundacion Ciencia para la Vida, Zanartu 1482, Santiago, Chile *Author for correspondence (e-mail: [email protected]) Accepted 8 April 2005 Development 132, 2587-2597 Published by The Company of Biologists 2005 doi:10.1242/dev.01857 Summary Migration of neural crest cells is an elaborate process that the Wnt receptor Frizzled7 (Fz7). Furthermore, loss- and requires the delamination of cells from an epithelium and gain-of-function experiments reveal that Wnt11 plays an cell movement into an extracellular matrix. In this work, it essential role in neural crest migration. Inhibition of neural is shown for the first time that the non-canonical Wnt crest migration by blocking Wnt11 activity can be rescued signalling [planar cell polarity (PCP) or Wnt-Ca2+] by intracellular activation of the non-canonical Wnt pathway controls migration of neural crest cells. By using pathway. When Wnt11 is expressed opposite its normal site specific Dsh mutants, we show that the canonical Wnt of expression, neural crest migration is blocked. Finally, signalling pathway is needed for neural crest induction, time-lapse analysis of cell movement and cell protrusion in while the non-canonical Wnt pathway is required for neural crest cultured in vitro shows that the PCP or Wnt- neural crest migration.
    [Show full text]
  • The Protection of the Human Embryo in Vitro
    Strasbourg, 19 June 2003 CDBI-CO-GT3 (2003) 13 STEERING COMMITTEE ON BIOETHICS (CDBI) THE PROTECTION OF THE HUMAN EMBRYO IN VITRO Report by the Working Party on the Protection of the Human Embryo and Fetus (CDBI-CO-GT3) Table of contents I. General introduction on the context and objectives of the report ............................................... 3 II. General concepts............................................................................................................................... 4 A. Biology of development ....................................................................................................................... 4 B. Philosophical views on the “nature” and status of the embryo............................................................ 4 C. The protection of the embryo............................................................................................................... 8 D. Commercialisation of the embryo and its parts ................................................................................... 9 E. The destiny of the embryo ................................................................................................................... 9 F. “Freedom of procreation” and instrumentalisation of women............................................................10 III. In vitro fertilisation (IVF).................................................................................................................. 12 A. Presentation of the procedure ...........................................................................................................12
    [Show full text]
  • Mitochondria Directly Influence Fertilisation Outcome in The
    REPRODUCTIONRESEARCH Mitochondria directly influence fertilisation outcome in the pig Shahinaz H El Shourbagy, Emma C Spikings, Mariana Freitas and Justin C St John The Mitochondrial and Reproductive Genetics Group, The Medical School, The University of Birmingham, Birmingham B15 2TT, UK Correspondence should be addressed to J C St John; Email: [email protected] S H El Shourbagy and E C Spikings contributed equally to this study Abstract The mitochondrion is explicitly involved in cytoplasmic regulation and is the cell’s major generator of ATP. Our aim was to determine whether mitochondria alone could influence fertilisation outcome. In vitro, oocyte competence can be assessed through the presence of glucose-6-phosphate dehydrogenase (G6PD) as indicated by the dye, brilliant cresyl blue (BCB). Using porcine in vitro fertilisation (IVF), we have assessed oocyte maturation, cytoplasmic volume, fertilisation outcome, mitochondrial number as determined by mtDNA copy number, and whether mitochondria are uniformly distributed between blastomeres of each embryo. After staining with BCB, we observed a significant difference in cytoplasmic volume between BCB positive (BCB1) and BCB negative (BCB2) oocytes. There was also a significant difference in mtDNA copy number between fertilised and unfertilised oocytes and unequal mitochondrial segregation between blastomeres during early cleavage stages. Furthermore, we have supplemented BCB2 oocytes with mitochondria from maternal relatives and observed a signifi- cant difference in fertilisation outcomes following both IVF and intracytoplasmic sperm injection (ICSI) between sup- plemented, sham-injected and non-treated BCB2 oocytes. We have therefore demonstrated a relationship between oocyte maturity, cytoplasmic volume, and fertilisation outcome and mitochondrial content. These data suggest that mitochondrial number is important for fertilisation outcome and embryonic development.
    [Show full text]
  • Totipotency Continuity from Zygote to Early Blastomeres: a Model Under Revision
    158 2 REPRODUCTIONREVIEW Totipotency continuity from zygote to early blastomeres: a model under revision Michele Boiani1, Ellen Casser1, Georg Fuellen2 and Elisabeth S Christians3 1Max Planck Institute for Molecular Biomedicine, Muenster, Germany, 2Rostock University Medical Center, Institute for Biostatistics and Informatics in Medicine and Aging Research (IBIMA), Rostock, Germany and 3Sorbonne Université, CNRS, Laboratoire de Biologie du Développement de Villefranche sur Mer (LBDV), Villefranche sur Mer, France Correspondence should be addressed to M Boiani or E S Christians; Email: [email protected] or [email protected] Abstract The mammalian zygote is a totipotent cell that generates all the cells of a new organism through embryonic development. However, if one asks about the totipotency of blastomeres after one or two zygotic divisions, opinions differ. As it is impossible to determine the individual developmental potency of early blastomeres in an intact embryo, experiments of blastomere isolation were conducted in various species, showing that two-cell blastomeres could give rise to a new organism when sister cells were separated. A mainstream interpretation was that each of the sister mammalian blastomeres was equally totipotent. However, reevaluation of those experiments raised some doubts about the real prevalence of cases in which this interpretation could truly be validated. We compiled experiments that tested the individual developmental potency of early mammalian blastomeres in a cell-autonomous way (i.e. excluding nuclear transfer and chimera production). We then confronted the developmental abilities with reported molecular differences between sister blastomeres. The reevaluated observations were at odds with the mainstream view: A viable two-cell embryo can already include one non-totipotent blastomere.
    [Show full text]
  • Lineage and Fate of Each Blastomere of the Eight-Cell Sea Urchin Embryo
    Downloaded from genesdev.cshlp.org on October 5, 2021 - Published by Cold Spring Harbor Laboratory Press Lineage and fate of each blastomere of the eight-cell sea urchin embryo R. Andrew Cameron, Barbara R. Hough-Evans, Roy J. Britten, ~ and Eric H. Davidson Division of Biology, California Institute of Technology, Pasadena, California 91125 USA A fluoresceinated lineage tracer was injected into individual blastomeres of eight-cell sea urchin (Strongylocentrotus purpuratus) embryos, and the location of the progeny of each blastomere was determined in the fully developed pluteus. Each blastomere gives rise to a unique portion of the advanced embryo. We confirm many of the classical assignments of cell fate along the animal-vegetal axis of the cleavage-stage embryo, and demonstrate that one blastomere of the animal quartet at the eight-cell stage lies nearest the future oral pole and the opposite one nearest the future aboral pole of the embryo. Clones of cells deriving from ectodermal founder cells always remain contiguous, while clones of cells descendant from the vegetal plate {i.e., gut, secondary mesenchyme) do not. The locations of ectodermal clones contributed by specific blastomeres require that the larval plane of bilateral symmetry lie approximately equidistant {i.e., at a 45 ° angle) from each of the first two cleavage planes. These results underscore the conclusion that many of the early spatial pattems of differential gene expression observed at the molecular level are specified in a clonal manner early in embryonic sea urchin development, and are each confined to cell lineages established during cleavage. [Key Words: Development; cell lineage; dye injection; axis specification] Received December 8, 1986; accepted December 24, 1986.
    [Show full text]
  • The Cleavage Stage Origin of Spemann's Organizer: Analysis Of
    Development 120, 1179-1189 (1994) 1179 Printed in Great Britain © The Company of Biologists Limited 1994 The cleavage stage origin of Spemann’s Organizer: analysis of the movements of blastomere clones before and during gastrulation in Xenopus Daniel V. Bauer1, Sen Huang2 and Sally A. Moody2,* 1Department of Anatomy and Cell Biology, University of Virginia 2Department of Anatomy and Neuroscience Program, The George Washington University Medical Center, 2300 I Street, NW Washington, DC 20037, USA *Author for correspondence SUMMARY Recent investigations into the roles of early regulatory the ventral animal clones extend across the entire dorsal genes, especially those resulting from mesoderm induction animal cap. These changes in the blastomere constituents or first expressed in the gastrula, reveal a need to elucidate of the animal cap during epiboly may contribute to the the developmental history of the cells in which their tran- changing capacity of the cap to respond to inductive growth scripts are expressed. Although fates both of the early blas- factors. Pregastrulation movements of clones also result in tomeres and of regions of the gastrula have been mapped, the B1 clone occupying the vegetal marginal zone to the relationship between the two sets of fate maps is not become the primary progenitor of the dorsal lip of the clear and the clonal origin of the regions of the stage 10 blastopore (Spemann’s Organizer). This report provides embryo are not known. We mapped the positions of each the fundamental descriptions of clone locations during the blastomere clone during several late blastula and early important periods of axis formation, mesoderm induction gastrula stages to show where and when these clones move.
    [Show full text]
  • 16. Early Embryo Develop 2008
    EarlyEarly EmbryonicEmbryonic DevelopmentDevelopment ZygoteZygote -- EmbryoEmbryo • two gametes fuse to produce zygote • with first division embryo is produced CleavageCleavage A series of mitotic divisions whereby a multicellular organism is formed – Cells produced are called blastomeres – Controlled by maternal mRNA and protein in most species – Most species = no net gain in volume • allows rapid division • is accomplished by skipping the G1 and G2 growth period between mitotic divisions MitosisMitosis PromotingPromoting FactorFactor • Regulates biphasic cycle of early blastomeres • Made up of two subunits – Cyclin B: accumulates during S phase and degrades following M phase – Cyclin-dependent kinase (cdc2): phosphorylates key proteins involved w/ mitosis CleavageCleavage • Rapid exponential increase in cell # – Frog egg divides into 37,000 cells in 43 hrs • 1 cleavage/hr – Drosophilia-50,000 cells in 12 hrs • 1 division every 10 mins for 2 hrs • Initially synchronous until mid-blastula transition – Growth phases added – Synchronicity lost – New mRNA transcribed Rate of formation of new cells in the frog Rana pipiens MechanismMechanism ofof MitosisMitosis • Result of two coordinated processes – Karyokinesis • Mitotic spindle of tubulin microtubules • Draws chromosomes to centrioles – Cytokinesis • Contractile ring of actin microfilaments • Creates cleavage furrow CleavageCleavage FurrowFurrow AmountAmount ofof YolkYolk inin OocyteOocyte • POLYLECITHAL or MEGALETHICAL - large amount of yolk – found in elasmobranchs, teleost fishes, reptiles,
    [Show full text]
  • Zygotes Segregate Entire Parental Genomes in Distinct Blastomere Lineages Causing Cleavage-Stage Chimerism and Mixoploidy
    Downloaded from genome.cshlp.org on October 2, 2021 - Published by Cold Spring Harbor Laboratory Press Research Zygotes segregate entire parental genomes in distinct blastomere lineages causing cleavage-stage chimerism and mixoploidy Aspasia Destouni,1,8 Masoud Zamani Esteki,2,8 Maaike Catteeuw,3 Olga Tšuiko,1,4 Eftychia Dimitriadou,1 Katrien Smits,3 Ants Kurg,4 Andres Salumets,5,6 Ann Van Soom,3 Thierry Voet,2,7,9 and Joris R. Vermeesch1,9 1Laboratory of Cytogenetics and Genome Research, Center of Human Genetics, KU Leuven, Leuven, 3000, Belgium; 2Laboratory of Reproductive Genomics, Center of Human Genetics, KU Leuven, Leuven, 3000, Belgium; 3Department of Obstetrics, Reproduction and Herd Health, Ghent University, Ghent, 9820, Belgium; 4Institute of Molecular and Cell Biology, Tartu University, Tartu, 51010, Estonia; 5Competence Centre on Health Technologies, Tartu, 50410, Estonia; 6Department of Obstetrics and Gynecology, University of Tartu, Tartu, 51014, Estonia; 7Sanger-EBI Single Cell Genomics Centre, Wellcome Trust Sanger Institute, Hinxton, Cambridge, CB10 1SA, United Kingdom Dramatic genome dynamics, such as chromosome instability, contribute to the remarkable genomic heterogeneity among the blastomeres comprising a single embryo during human preimplantation development. This heterogeneity, when com- patible with life, manifests as constitutional mosaicism, chimerism, and mixoploidy in live-born individuals. Chimerism and mixoploidy are defined by the presence of cell lineages with different parental genomes or different ploidy states in a single individual, respectively. Our knowledge of their mechanistic origin results from indirect observations, often when the cell lineages have been subject to rigorous selective pressure during development. Here, we applied haplarithmisis to infer the haplotypes and the copy number of parental genomes in 116 single blastomeres comprising entire preimplantation bovine embryos (n = 23) following in vitro fertilization.
    [Show full text]
  • Snail2 Controls Mesodermal BMP/Wnt Induction of Neural Crest Jianli Shi1, Courtney Severson1, Jianxia Yang1,*, Doris Wedlich1,2 and Michael W
    RESEARCH ARTICLE 3135 Development 138, 3135-3145 (2011) doi:10.1242/dev.064394 © 2011. Published by The Company of Biologists Ltd Snail2 controls mesodermal BMP/Wnt induction of neural crest Jianli Shi1, Courtney Severson1, Jianxia Yang1,*, Doris Wedlich1,2 and Michael W. Klymkowsky1,† SUMMARY The neural crest is an induced tissue that is unique to vertebrates. In the clawed frog Xenopus laevis, neural crest induction depends on signals secreted from the prospective dorsolateral mesodermal zone during gastrulation. The transcription factors Snail2 (Slug), Snail1 and Twist1 are expressed in this region. It is known that Snail2 and Twist1 are required for both mesoderm formation and neural crest induction. Using targeted blastomere injection, morpholino-based loss of function and explant studies, we show that: (1) Snail1 is also required for mesoderm and neural crest formation; (2) loss of snail1, snail2 or twist1 function in the C2/C3 lineage of 32-cell embryos blocks mesoderm formation, but neural crest is lost only in the case of snail2 loss of function; (3) snail2 mutant loss of neural crest involves mesoderm-derived secreted factors and can be rescued synergistically by bmp4 and wnt8 RNAs; and (4) loss of snail2 activity leads to changes in the RNA levels of a number of BMP and Wnt agonists and antagonists. Taken together, these results identify Snail2 as a key regulator of the signals involved in mesodermal induction of neural crest. KEY WORDS: Snail2, Slug, Snail1, Twist1, Mesoderm, Neural crest induction, BMP, Wnt, Xenopus INTRODUCTION The transcription factors Snail and Twist were first identified in Neural crest is of interest for both evolutionary and medical Drosophila melanogaster, where they sit at the end of the Toll/Dorsal reasons.
    [Show full text]
  • Animal Development.Pdf
    Animal Development All living organisms exhibit some form of growth and egg sperm development. Members of the animal kingdom have the most zygote (fertilized egg) complex developmental cycles of any living organism. cleavage preembryonic blastula stages The sequence of discrete, recognizable stages that gastrula these organism pass through as they develop from the formation of a zygote (the fertilized egg) to embryonic stages the sexually mature adult are referred to as its developmental cycle. larva nymph fetus Animal development can be subdivided into several sequential processes: 1. Gametes. gametogenesis fertilization The gametes are produced by the process of preembryonic development meiosis which differs from mitosis in that only embryonic development one of each chromosome ends up in the cells post embryonic development after division. Embryonic development includes the processes of The male gamete, the sperm, is small and almost growth, determination, differentiation and always flagellated. morphogenesis. The female gamete us usually large since it contains yolk, and spherical. 2. Fertilization. 1 2 At fertilization only a single sperm penetrates and fertilizes the egg to produce a zygote. The egg Slide: starfish early cleavage wm (Fig. and sperm each contribute a set of chromosomes 4.2) so that the fertilized egg then has a pair of each chromosomes, one set from the male parent and -observe the slide of starfish eggs in early the other set from the female parent. To prevent cleavage and be able to distinguish this stage additional sperm from penetrating the egg a from those that follow fertilization cone is produced to produce the original -note 2, 4, 8 cell stages; each cell is sperm into the egg quickly.
    [Show full text]